Radio receiving system



June 30, 1936. H. F. DALPAYRAT RADIO RECEIVING SYSTEM Filed Feb. 5, 1935 INVENTOR HENRI 'FRANQOIS DALPAYRAT ATTORNEY Patented June 30, 1936 UNITED STATES PATENT OFFICE RADIO RECEIVING SYSTEM Application February 5, 1935, Serial No. 5,011

10 Claims.

My invention relates to radio receivers, more particularly to regenerative receiving systems and has for its object to improve the performance and stability of systems of this type.

In the known regenerative radio circuits, part of the amplified signalling current variations in the output circuit of an amplifying device such as an electronic relay is returned or fed back to the input circuit for renewed amplification this being equivalent to a decrease of the effective resistance and the losses in the input circuit and a corresponding increase of the signaling current strength and the selectivity with respect to different carrier frequencies or wave lengths of the receiving signals. Since the feed back energy is again amplified it causes in turn an increased feed back current applied to the input circuit in such a manner that the operation of such a system is cumulative and has a tendency to become unstable especially under varying receiving conditions such as varying receiving signal intensity and varying frequency as in the case of the normal operation of radio broadcast receivers. This makes it impossible or difficult to maintain stable operating conditions and to prevent signal distortions or occasional self-oscillation of the receiver, causing disturbing howling and hissing noises, as is well known. For this reason, as is well known, regenerative receivers are diflicult to operate and require a certain amount of skill on the part of the broadcast listener or operator.

The improved circuit according to the invention overcomes the above difficulties and insures stable operation and substantially equal regenerating conditions over an extended operating range, thus making possible the operation of regenerative receivers by unskilled persons and insuring maximum signal strength and selectivity in a most simple and efiicient manner with a minimum of circuit elements and operating adjustments. 1

Further objects and aspects of the invention will become apparent from the following detailed description taken with reference to the accompanying drawing illustrating a regenerative receiving circuit for broadcast receivers and the like according to the invention.

Referring to the drawing, I have shown an antenna circuit for receiving incoming modulated high frequency oscillations comprising an antenna I in series with an antenna condenser 2, a coupling impedance such as a high ohmic resistance 3 and a ground connection shown at 4. The signalling potential variations produced by the coupling element 3 are applied to the grid 1 and the grounded cathode 6 of a first aperiodic high frequency amplifier tube 5 in a known manner. The tube 5 furthermore comprises a screen grid 8, a suppressor grid 9, an anode l0, and a heater winding 6' for raising and maintaining the cathode 6 at electron emitting temperature.

Item l2 represents a biasing resistance in the cathode lead of the tube shunted by an equalizing condenser [3 for producing the proper biasing operating potential for the grid 7 with respect to the cathode 6 in a known manner. The suppressor grid 9 is directly connected to the cathode 6 and the screen grid 1 is shown to be connected to the positive pole or a high tension operating source indicated by the plus sign in the drawing through a voltage drop resistance l4 and shunted to ground by means of a decoupling condenser l 5 in a manner well known in the design of radio circuits. The anode I0 is connected to the positive pole of the high potential source through a high frequency choke coil 25 for supplying the space discharge current of the tube.

In this manner incoming high frequency oscillations applied to the grid 1 cause corresponding. amplified current variations in the anode circuit which in turn are applied to a multiple tuned circuit through a coupling condenser 25. The tuned circuit is comprised of an inductance coil 26 and parallel condenser 21 inserted in the anode circuit of the tube and serves as a coupling element for applying the amplified signal current variations to the next regenerative detector stage. For this purpose it is coupled to the grid N3 of the regenerative amplifying tube l6 according to the invention through a grid coupling condenser 36 and a grid leak 3| whereby the tube [6 acts as a detector for separating the modulating or audio signal variations from the high frequency or carrier oscillations in a known manner. The tube l6 furthermore comprises an indirectly heated cathode IT with a heater IT, a positive or screen grid IS, an anode 2| and a further grid 20 between the screen grid I 9 and the anode 2|. As a second grid 20 to serve as a further control element for the electron stream the. suppressor grid provided in the known type of triple grid or pentode tubes may be used for satisfactory results. The anode 2| is connected to the positive pole of the high tension source through a high frequency choke coil 34 shunted by a high ohmic resistance 34' in series with an audio frequency choke coil 36 serving as a coupling element for applying the audio frequency current variations to the next following audio stage comprised of the tube 42. I have furthermore shown the positive or screen grid 19 connected to the positive pole of the high tension source through a pair of drop resistors one being fixed and shown at 32 and the other being variable and having one end thereof connected to ground as shown at 39. The latter serves as a volume control element by varying the positive potential applied to the screen grid [9. The latter grid I9 is furthermore connected in a known manner to ground through a decoupling condenser 33.

Regeneration of the input signals applied to the tube 16 is obtained through a feed back cir cuit connected between the anode 2| and ground or cathode including a condenser 28' in series with a feed back or tickler coil 28 inductively coupled with the induction coil 2.6 of the tuned circuit. In this manner amplified current vari-'- ations in the anode or output circuit of the tube are returned or fed back into the input circuit 26, 27 for further amplification and increase of the signal strength and selectivity of the circuit.

In order to stabilize and maintain the degree of amplification or regeneration substantially even over an extended range of receiving frequencies and within. a predetermined. intensity range of the received signals, I have shown the incoming and regenerated signalling oscillations in the tuned circuit 26, 21 applied to at least two grids in different phase relation in such a manner that one grid acts to. check or stabilize the function. of the other grid so as to main: tain a substantially even or uniform degree of regeneration over a wide range of receiving frequencies and incoming signal intensity and to prevent any excessive variations and consequent instability in the performance and function of the circuit. For this purpose the tuned circuit 26,. is coupled to the input grid 18 through the condenser 30 on the one hand as pointed out and to the second control grid 28 through a ohmic resistance 29 on the other hand. Since the condenser 30 reverses the potential applied to it itis seen that the potentials applied to the grids l8 and 20 from the tuned circuit are of substantially opposite phase the, first one beinga regencrating potential and serving to increase the signal' strength and theother acting as a neutralizing or degenerating potential for stabilizing and limiting the regeneration and preventing it from becoming excessive and causing distortions. or self-sustained oscillations in the tuned circuit. In my co-pending application entitled Radio circuits, Serial No. 151,813, I, have disclosed a stabilizing regenerative system comprising means for applying regenerating and degenerating potential variations to separate grid electrodes placed in a single electron stream. The present invention relates to an improved and simplified circuit arrangement over the circuit disclosed in the above application insuring ahighly stable operation and equal response over a wide operating range such as the broadcast receiving range and covering a, wide intensity range of the receiving signals. As is understood and pointed out inthe above mentioned co-pending application, the provision of regenerating and degencrating potentials acting purely electronically on the operation of the tube; that is, through separate grid electrodes suitably placed in the electron stream, allows of an accurate adjustment of the regenerating and degenerating potentials substantially independently and without interference, thus insuring a stable and uniform operation and'per-formance of the system. While iii-the above mentioned applicationcompletely separate regenerating and degenerating feed back paths are shown, I have found that the performance and signal strength is increased and the circuit and its operation greatly simplified by partly using a common feed back path as shown by the present application comprised of the feed back condenser 28, feed back coil 26 to initially secure efficient regeneration and then to divide the regenerated current variations upon the separate grids l8 and 20 in proper phase relationship as described.

is greatly simplified while insuring stability and uniform and efficient operation over an extended range of varying operating conditions such as varying frequency and intensity of the receiving signals.

The screen grid l9 in addition to its normal function in increasing the amplification factor and suppressing capacitative feed back between the plate and control grid of the tube furthermore serves in the circuit as disclosed as a means for producing a space charge in the space between the scren grid and the anode by slowing down the electrons having passed through the screen meshes. due to the attracting force of the positive screenpotential. The slowing down of the electron, speed is equivalent to an increased space charge or a virtual cathode, resulting in increased effectiveness of the controlling function of the degenerating or neutralizing electrode 28 on the discharge stream.

I, have furthermore found it advisable in order to. equalize the performance and to secure sub stantially even response over the operating frequency range to provide a shunt condenser of small capacity 23. between the anode and the cathode of the tube and a high ohmic impedance 34 shunting the high frequency choke coil 34 in the anode circuit. The function of the condenser 23 in preventing excessive regeneration and oscillations for the shorter wave length range is due obviously to a by-passing of the shorter wavelengths or higher frequencies and corresponding decrease of the feed back or regenerating currents through the feed back path 26, 28. The function of the resistance 34 is to broaden the tuning of the choke coil 34 and prevent excessive, regeneration or self-oscillations for the lower receiving frequency signals.

The remainder of the circuit is of standard design comprising a further amplifying tube .2 having anindirectly heated cathode 1 3 provided with a heater 43, a control grid M, screen grid 45 and an anode 46. The audio or modulating signal variations in the output circuit of the regenerative detector H5 are applied from the coupling choke coil to the grid 34 of the audio amplifier 42 through a coupling condenser 35 and grid leak resistance 31 in a known manner. The amplified audio signalling currents may be utilized in a known manner such as for operating aloud speaker 5| through an audio transformer 5!]: The screen grid 45 and anode A6 are shown directly connected to the positive pole of the high tension source. Item 41 represents a cathode lead resistance shunted by a decoupling condenser i8 for securing the proper operating biasing potential for the grid 44, and as represents a by-pass condenser for the anode circuit arranged in a known manner.

I have furthermore shown a resistance 33 shunting the coupling choke coil 38 to increase its damping and to prevent the excitation of audio frequency oscillations due to inherent audio resonant characteristics of thecircuit.

In this manner the arrangement of the circuit and its adjustment The circuit illustrated is adapted for operation from both an alternating current or direct ourrent source and furthermore comprises a rectifying tube 55 having a pair of rectifying discharge paths comprised respectively of the cathode 55 and anode 58 on the one hand and cathode 51 and anode 59 on the other hand, the cathodes being provided with a common heater 56' in the known manner. The anodes 58 and 59 are connected to the plus pole of the high tension operating source 69 in case of a direct current operation. The cathode 56 of one rectifying path is connected through a smoothing choke coil 63 associated with a pair of grounded filter condensers 6d and 55 to the anode or screen grid potential points of the receiver as disclosed. Items 66 and 61 represent an equalizing resistor and a decoupling condenser connected between the positive potential point of the rectifier and ground in a well known manner. The second rectifying path 51, 59 serves to supply the exciting current for the loud speaker 5|. For this purpose the oath-- ode 51 is shown connected to a terminal of the exciting winding 52 shunted by a smoothing condenser 63, the remaining terminal of the winding 52 being connected to ground as shown. The heaters for the separate tubes are connected in series together with a suitable voltage drop resistance 6| and heated from the common supply source as shown by the separate heating circuit in the drawing.

While I have shown the invention as embodied in a specific circuit arrangement, it is understood that variations and modifications may be made coming within the broader spirit and scope of the invention as expressed in the appended claims.

I claim:

1. A regenerative radio circuit comprising a space discharge amplifier having output electrodes and a first space current control element; an input circuit connected to said control element; an output circuit connected to said output electrodes; means for feeding back amplified signal current variations from said output circuit to said input circuit; a second space current control element also connected to said input circuit; and means for securing a predetermined phase relation of the control potentials applied to said first and second control elements from said input circuit, and means for preventing mutual coupling between said first and second control elements.

2. A regenerative radio circuit comprising a space discharge device having a cathode, anode and a first control grid; an input circuit connected to said grid and an output circuit connected to said anode; feed back means for applying regenerating potential variations from said output circuit to said input circuit; a second grid electrode and circuit connections therefrom to said input circuit; and means for varying the phase relation of the potentials applied to said grid electrodes from said input circuit, and means for preventing electrostatic coupling between said first and second grid electrodes.

3. A regenerative radio circuit comprising a space discharge device having a cathode, anode and a first grid; a tuned input circuit; a capacitative circuit connection from said tuned input circuit to said grid; an output circuit connected to said anode; a regenerative circuit interconnecting said output circuit and said input circuit; a further control grid for said device; a conductive circuit connection therefrom to said input circuit, and means for preventing electrostatic coupling between said first and second grid.

4. A regenerative radio circuit comprising a space discharge device having a cathode, an anode and a first grid; a tuned input circuit; a capacitative circuit connection from said tuned circuit to said grid; an output circuit connected to said anode; a regenerative circuit interconnecting said output circuit and said input circuit; a further control grid for said device; a conductive circuit connection therefrom to said input circuit including a high ohmic resistance, and means for preventing electrostatic coupling between said first and second grid.

5. A regenerative circuit comprising a space discharge amplifier having a cathode, an anode, and a first grid; a tuned input circuit connected to said grid through a grid condenser; an output circuit connected to said anode; a feed back circuit from said output circuit to said in ut circuit; a further control grid and a conductive circuit connection therefrom to said input circuit; and a screen electrode arranged intermediate said grid electrodes and means for maintaining said screen at a positive potential with respect to said grid electrodes.

6. A regenerative detector circuit comprising a space discharge device having a cathode and an anode and a first control grid; an input circuit connected to said grid through a grid condenser and a grid leak device; an output circuit connected to said anode; a regenerative circuit interconnecting said anode and cathode and including a condenser in series with an induction coil coupled with said input circuit; a further control grid and a conductive circuit connection therefrom to said input circuit including a high ohmic resistance, and a screen grid arranged between said first and second control grids.

7. In a regenerative circuit as claimed in claim 6 including a by-pass capacity between said anode and cathode and a high frequency choke coil in series with the anode lead shunted by high ohmic resistance.

8. A regenerative detector circuit comprising an amplifying tube having a cathode and a pair of control grids; a screen arranged intermediate said control grids; means for maintaining said screen at a positive potential with respect to said grids; a tuned input circuit connected to one of said control grids through a grid coupling condenser and a grid leak resistance; an output circuit connected to said anode; a regenerating circuit path between said output and said input circuits and a high ohmic resistance connecting said input circuit and said second control grid.

9. A regenerative detector circuit comprising a vacuum tube having a cathode, anode and a first control grid near said cathode; a parallel tuned input circuit; a capacitative circuit connection from one terminal of said circuit to said grid; a direct connection from the other terminal of said circuit to said cathode; a grid leak resistance connected to said control grid; an output circuit connected to said anode; a regenerative circuit interconnecting said output circuit and said input circuit; a second control grid for said tube; a conductive circuit from said second grid to the terminal of said input circuit connected to said first grid, and screening means to prevent capacitative coupling between said first and second control grids.

10. A regenerative detector circuit comprising a vacuum tube having a cathode, anode and a first grid electrode near said cathode; a parallel tuned input circuit; a capacitative circuit connection from one terminal of said circuit to said grid; 2. direct connection from the other terminal of said circuit to said cathode; a grid leak resistance connected to said control grid; an output circuit connected to said anode; a regenerative circuit interconnecting said output circuit and said input circuit; a second grid for said tube; a

conductive circuit connection including a high ohmic resistance from said second grid to the terminal of said input circuit connected to said first grid and a screen grid arranged intermediate said control grids and means for maintaining said screen grid at a positive potential with respect to said control grids.

HENRI FRANCOIS DALPAYRAT. 

